Method of heating up and initiating metallurgical reactions in the pouring jet when degasifying the latter in a vacuum



3,511,641 CTIONS' May 12, 1970 w. COUPETTE METHOD OF HEATING UP AND INITIATING METALLURGICAL REA IN THE POURING JET WHEN DEGASIFYING THE LATTER IN A VACUUM Filed Aug. 5, 1966 United States Patent US. Cl. 75-12 4 Claims ABSTRACT OF THE DISCLOSURE Heated plasma gases are directed upon the falling droplets of molten metal formed by vacuum. stream degassing thereof. The plasma gases serve to minimize the metals heat losses during vacuum treatment. Also reactive gases can be utilized as the plasma when metallurigical reactions are desired.

The present invention relates to a method of heating up the pouring jet or stream and for initiating metallurgical reactions in the pouring jet or stream when degasifying the same in a vacuum.

When degasifying a pouring jet or stream in a vacuum, relatively high disturbing temperature losses occur during the degasification process. In an effort to reduce these heat losses and thus to reduce the disadvantageous consequences of the cooling off of the pouring jet or stream, it has heretofore been the practice to preheat the pouring ladle and/or the vacuum container, and/or additionally to heat said pouring ladle or vacuum container during the pouring operation. While these steps have somewhat reduced theheat losses, they have been unable to completely prevent the same.

It has also been attempted following the degasification process proper to permit certain metallurgical reactions in the pouring jet or stream in a vacuum, and to do so by introducing solid substances or a foreign gas into the vacuum or into the pouring ladle. However, it has been found that the desired various reactions of the introduced foreign gases do not occur with liquid steel in the desired manner. This is especially the case when reactions with finest droplets are involved which preferably occur when employing a high vacuum or when treating non-quiet or rimmed steel.

It is, therefore, an object of the present invention to provide a method of heating up and initiating metallurgical reactions in the pouring jet or stream when degasifying the latter in a vacuum, which will overcome the above mentioned dawbacks.

It is another object of this invention to provide a method as set forth above, which will practically prevent any heat losses of the pouring jet or stream.

It is a further object of this invention to provide a method as set forth above, which will greatly intensify the metallurgical reactions, i.e. a deoxidation, a decarburization, a dehydration or a denitration, of the jet stream while permitting the further utilization of the heretofore employed pouring ladles, degasifying vessels as well as the vacuum creating devices, and the like.

These and other objects and advantages of the invention will appear more clearly from the following specification in connection with the accompanying drawing diagrammatically illustrating an apparatus according to the invention for carrying out the method of this invention.

The above mentioned objects have been realized by flowing a plasma gas around the pouring jet while the latter is entering the vessel in which the degasification "ice takes place and in which a pressure below atmospheric pressure is maintained. The degasification vessel is equipped with one or more adjustable plasma burner means the axis or axes of which are directed toward the pouring jet. Preferably, the plasma burner means are arranged in the upper portion of said vessel.

Modern plasma burners have outputs up to many thousands of kilowatts and are able to produce gas temperatures up to 50,000 C. in an operation-safe manner.

For purposes of degasification, small steel droplets down to a size of 0.5 millimeter are desirable in the vacuum chamber so that the relatively large surface of said steel droplets will be heated up by the heat of the introduced gas plasma while during the degasification process heat losses with their disadvantageous results, such as increased viscosity and decreased reaction of the fine steel droplets, will be prevented.

When the plasma burner means are operated with inert gases, such as argon, the otherwise occurring heat losses will be made up and, more specifically, by the extremely intensive radiation in the vacuum and by the convection of the plasma gases at the extremely high temperatures. Furthermore, the degasification aiding advantage will be obtained that the blown-in inert gas will form the surface of the steel droplets wash away the gas which during the vacuum treatment escapes from the droplets.

For purposes of producing additional metallurgical reactions, such as deoxidation, decarburization, deyhydration or denitration of the steel, it is advantageous in the vacuum gas metallurgy that all reaction. products forming at the border layers be withdrawn immediately so that they cannot react against each other.

When instead of inert gas, reactive plasma gas is employed, as for instance hydrogen, oxygen, methane, carbon tetrachloride, chlorine, sodium vapor, or the like, or mixtures thereof, and are 'by means of plasma burners directed toward the pouring jet or stream in the degasification vessel and impart upon the pouring jet or stream at high speed while flowing around the individual droplets of the pouring jet or stream, an intensive and quick reaction of the steel droplets with the gas flowing therearound will be obtained in view of the extremely high temperatures of the plasma gases at the phase limits of the steel droplets passed around by the plasma gas. The energy of the said reaction of the steel droplets with the gas flowing therearound is extremely high because in addition to the specific heat due to the extremely high temperature, the dissociation energy with multi-atomic gases, and generally the ionization energy in the plasma jet or stream will be added.

In order to increase the reaction effect of the reactive plasma gases, contact substances may be added to the plasma gases. Such contact substances are for instance calcium, cobalt, vanadium, tungsten, or titanium, which are added in low quantities of from approximately 10 to 25% of the weight of the gases. .T he higher the atomic weight of said substance, the less quantity of the contact substance has to be added.

When employing hydrogen in plasma condition for purposes of deoxidation of the pouring jet of non-quieted steel, water steam will form which will represent only a slight load on the pumping system producing the vacuum. This is due to the fact that modern pouring jet gas installations are due to the considerable volume of the gas to be withdrawn equipped only with multi-stage steam jet vacuum pumps while the Withdrawn water steam is condensed in the condenser following the first ejector stage. For the metallurgical reaction it is important that only gaseous products are formed which cannot contaminate the steel, and that the formed reaction products are as quickly as possible withdrawn from the 3 range of the pouring jet or stream by means of a vacuum pump. Experience has shown that with the method according to the present invention gas metallurgical reactions can be carried out in a simple and economic manner without having to resort to the previously required and strongly interfering metallurgical slags.

The employment of one or more plasma burners yields the further advantage that the degasification vessel with the pouring ladle therein Will be kept hot during the treatment intervals.

Referring now to the drawing in detail, the apparatus shown therein comprises a degassification vessel having a connection 2 adapted to be connected to a vacuum pump (not illustrated). The degasification vessel 1 is airtight and by means of a detachable cover 3 and the pur ing ladle resting thereon is closed in an air-tight manner. Within the degasification vessel 1 there is provided a ladle 6 which receives the steel after it has been degasified in the steel jet or stream, said steel being poured out of the ladle 5. In the cover 3 of the degasification vessel 1 there are provided one or a plurality of plasma burners 4 in such a way that the axes thereof are directed toward the axis of the pouring jet. The plasma burner or burners 4 are for purposes of controlling the quantity of the gas to be converted into plasma condition and for purposes of changing the temperature thereof equipped with control devices. The burners are preferably mounted on cover 3 or in the upper portion of the vessel 1 and are so adjustable selectively by suitably operable means that the plasma flame is preferably or can preferably be directed onto the upper portion of the pouring jet or stream.

With a 100 ton melt, for instance, which is to be degasified in a pouring jet or stream, plasma burners with from 1000 to 2000 kilowatt output will suffice. In order not to place the vacuum pump under unnecessary loads, very high gas temperatures are selected so that a high heat supply can be obtained with a relatively small quantity of plasma gas at a temperature with in the range of from 20,000 to 40,000 C. Advantageously, the quantity of the introduced plasma gas should not exceed of the power of the vacuum pump.

It is, of course, to be understood that the present invention is, by no means, limited to the particular method and apparatus described herein before, but also comprises any modifications within the scope of the appended claims.

Plasma burners and adjusting means associated therewith for adjusting such burners may be of any desired standard type, as for instance of the type disclosed in French Pat. No. 1,311,252-La Soudure Electrique Autogene, Procedes Arcos, Belge and in pamphlet No, 150 ARCOS hausmitteilungen der ARCOS-Gesellschaft fiir Schweisstechnik mbH., Aachen.

The vacuum to be maintained in the degasification vessel may be Within the range of the vacuum employed with heretofore known degasification processes efiected in a vacuum. Preferably the vacuum should be within 5 the range of from 0.1 to about 30 mm. Hg.

The opening and closing of the pouring ladle 5 may be etfected in customary manner by opening and closing the opening 7 by means of a closure member 8, e.g. a stopper rod.

What I claim is:

1. A process for stream degassing molten metal, comprising: feeding said molten metal to a vacuum chamber as a pouring stream, maintaining said chamber at sufficient vacuum to cause the molten metal in said pouring stream to disperse into small droplets as it passes into the vacuum chamber, directing a stream of hot plasma gases amongst the droplets as they pass through the vacuum chamber, and subsequently collecting the degassed molten metal.

2. A method according to claim 1 comprising introducing said hot plasma gas into said vessel in the form of jets directed toward the pouring stream being degasified.

3. A method according to claim 1 comprising introducing a reactive plasma gas consisting of at least one gas selected from the group which consists of hydrogen, oxygen, methane, carbon tetrachloride, chlorine and sodium vapor for the purpose of creating metallurgical reactions in the pouring stream.

4. A method according to claim 3 comprising adding to the reactive plasma gas at least one contact substance selected from the group consisting of calcium, cobalt, vanadium, tungsten and titanium, the quantity of the added contact substance amounting to from 10% to 25% of the weight of the gas.

' References Cited UNITED STATES PATENTS 40 Re. 24,821 5/1960 Staufi'er 164-64 X 2,909,422 10/1959 Schwabe 75-12 X 2,997,3 86 8/ 1961 Feichtinger.

- 3,060,015 10/1962 SpOlderS et a1. 75-49 X 3,084,037 4/1963 Smith l646l X 3,251,680 5/1966 Goss et a1. 7512 X 3,257,197 6/1966 Death et a1 7510 X 3,279,912 10/1966 Death et al. 75-10 3,288,594 11/1966 Smith 7593 X 3,342,250 9/ 1967 Treppschuh et a1.

HENRY w. TARRING II, Primary Examiner U.S. Cl. X.R. 

